During drilling operations of subsurface wells, such as hydrocarbon wells or water injection wells, there is a need for communication between the well and the surface. In many situations it is desired to monitor the pressure in the bottom and, if possible, also along the well. In this case sensors are located in the bottom and/or along the drill pipe system.
The common way of transferring signals through a drill pipe system is to use so-called mud pulse telemetry, where a valve located in the bottom of the drill pipe system is throttled in short periods and thereby pressure pulses are generated. The pressure pulses propagate through the mud/fluid to the surface of the well, where the pressure pulses are measured and converted to electrical signals etc.
This type of equipment are often assembled of a number of modules, such as a pulse sending module, a turbine module using the fluid flow for producing electrical power, a number of sensing modules and directional drilling equipment.
There are several disadvantages with this type of technology. First of all, the data rate is low, typically 10 bits/second and decreasing with the length of the drilling pipe. Moreover, the drilling fluid can not be too compressible, i.e. contain too much gas. The pressure pulses also disturb the pressure control and measurements in the well. At last, an active fluid flow is necessary for the communication, i.e. no information can be retrieved while the flow is stopped to connect new drill pipes at the top. Another difficult situation is the well shut inn, when it is important to receive information and the solution with signals transmitted with mud pulses will not provide this during well shut in.
Alternative drilling pipe systems is known, for example from WO 2009/011594.
Such a drilling pipe system comprises a first pipe provided concentric inside a second pipe by means of hanging devices, where one fluid is transferred down into the well in the compartment between the first pipe and the second pipe, and where the fluid together with cuttings etc from the drilling operation is transferred up in the compartment within the first pipe.
The object of the invention is to provide an improved method and system for transferring signals through a drill pipe system.